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MG MGA - alternator

Strange question. My MGA was previously converted to an alternator. To engage the alternator, I have to pull the fog switch out and then off just after starting. Anyone know why?
rjb babylon

normally when you have an alternator fitted, it works as soon as you start the engine. In other words, the engine should start and the ignition light should go out which shows you that the alternator is charging the battery.

So do you mean that your ignition light doesn't go out until the fog light switch is switched on?

If that is the case then your car has been wired up in a very strange way!

To check your alternators wiring have a look at the MGA GURU website and you will see how an alternator should be wired up.

It is a very simple wiring up job when compared to the generator.

c firth

Not wired right...but very interesting! :-)
Steven Devine

Thanks for the input. The charging light does not go on. I sent the car back to the dealer as soon as it was off the truck due to the charging issue and numerous other issues that were not shown in photos or descriptions. I am still trying to work a solution with the dealer. He already has my money.
rjb babylon


Just making certain that you have this right, the ignition light illuminates when you switch the ignition on.
It should then go off as soon as the engine starts.

If the ignition light stays illuminated when the engine is running you either have a alternator fault or a fault in its wiring.
You shouldnt have to switch anything else on to make it work.

c firth

The charging light may be your problem. The alternator needs a small "seed" voltage to "start" the alternator generating its own voltage. This is usually provided by the current through the charging light. I have seen alternator "failure" due to a blown out charging bulb.

For the same reason, the alternator will not even attempt to charge a zero volt battery.
F. J. Bruns

I'm with Bruns. When I fitted an alternator to my Y-type it failed to charge due to a faulty charging bulb holder.
Willem van der Veer

I understand you no longer have possession of the car. Have the dealer turn on the ignition without starting the car. The ignition light should come on. If not, there is your problem. If it does, trace the SMALL wire from the alternator. it should go the yellow wire from the ignition warning light. (if the control box is still there (I never recommend leaving the useless box installed) the wires probably connect at the "D" terminal. In any case, there should be a connection from the ignition switch to one side of the Ignition warning light. The other side of the light should connect to the SMALL wire in the alternator.

My guess is that (somehow) turning on the fog light provides the "seed" voltage to the alternator.
F. J. Bruns

This thread was discussed between 30/09/2015 and 02/10/2015

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